Many yield point enhancer are known, such as the amide resin additives disclosed in U.S. Pat. No. 4,816,551.
Oil based muds containing such amide resin additives exhibit high solids carrying capacity but also show increasing values of viscosity when exposed to low temperatures; their use for off-shore deep sea drilling operation is therefore mostly critical.
For offshore operation the low temperature of the sea is always to be taken into account, as the effect of the yield point enhancers is usually strongly dependent from temperature (the lowest the temperature, the highest the risk of undesired gelling of the mud).
Drilling operations are not continuous processes; many stops must necessarily take place and it is then that the risk of an excessive viscosity of the mud, due to the presence of a yield point enhancer, can create serious problems.
When drilling operation takes place in non-deep water, particular caution and additional tests are required to correctly dose the yield point enhancer.
When deep water drilling operations are performed, the temperature of the sea falls near to zero Celsius degrees, and the risk of gelling of the mud is very high, especially during stops.
It would therefore be highly desirable to find a self-breakable yield point enhancer for oil based drilling muds showing high solids carrying capacity during transportation and whose viscosifying effect ceases as soon as drilling actually takes place, thus leaving the rheology control of the mud to the organophilic clays.